For example, in the case where a contamination of a fluid such as an engine oil is measured, there is known a method of measuring a degree of contamination based on a transmittance obtained by irradiating the fluid with an inspection light.
As a specific example, as disclosed in Patent Literature 1, there is a configuration such that, a projection optical system member provided with a projection port for projecting an inspection light and a light-receiving optical system member provided with an introduction port for receiving the inspection light are respectively attached to opposing surfaces of a cell so that the inspection light projected from the projection port passes through a fluid inside the cell via a window of the cell so as to be received by the introduction port.
By the way, for example, in such a case of measuring a degree of contamination of a cleaning chemical solution for cleaning a semiconductor wafer, it is necessary to use a corrosion-resistant material such as PTFE (Teflon) as a cell material.
However, since PTFE has a large rate of change in shape with respect to a temperature change, with an aspect of the projection optical system member and the light-receiving optical member attached to the cell as mentioned above, in the case where chemical solutions at various temperatures are used as in the case of, e.g., a sheet-type semiconductor manufacturing apparatus, etc., the cell is deformed due to differences in temperature of every chemical solution so as to cause such as a shift between an optical axis of the projection optical system member and that of the light-receiving system member, and therefore the measurement accuracy cannot be ensured.
Citation List
Patent Literature
Patent Literature 1: JP2007-93598A